The actual representation as practiced today per hai di zhen (needle at sea bottom) is literal where right hand is going downward where a logical explanation is hand going towards qihai/dantian (groin) or lower, whicn may not be actual use. It apears most people only know about this literal explanation so in this sense, it has reality (albeit its own).

The metaphor is that the "sea bottom point location" may have been "lost" meaning no one may be aware of its actual position, or, it has roots in classical "Daoist" acupuncture, or even modern acupuncture for that matter i snot discussed-I do not know.I will not venture to say it is "secret"-only that people do not talk about it openly.My last two statements follow each other like night and day, wherether they mean the same thing is left to the wind.

All I am saying is the common meaning (what most people say it is) is distinct from its physical "esoteric" reality, though they may share a common thread.

At this point I cannot prove my asertion on location but I will try in the near future to give a reference for you to check since your Mandarin ability far exceeds mine.

You wrote, > In "Needle at Sea Bottom" when one bends the torso to go downwards, <

From everything I know in Tai Chi Chuan and physiology this is bad form. There is a waist turn, but don't bend at the waist because this puts too much pressure on the lower part of the spine. Do it with your back straight.

You make an excellent point about the posture. Although Yang Chengfu's description speaks of "folding the waist and sinking downward," this is another case where the designation "waist" is misleading in English. The "folding" is actually done at the pelvis joints, with the spine remaining straight, though inclining forward. The photo of Yang Chengfu's posture shows this. I seem to recall that Fu Zhongwen's more modern description was clearer about this.